Nikola Tesla's Electrical Isochronous Oscillators
Capacitive Discharge Power Processing
Tesla's Houston Street Laboratory Illuminated Using Patent 514,168 - Note the wireless receiver table right lower front.
See Tesla's article in: Electrical Experimenter, July 1919
454,622
System of Electric Lighting - Apr 25, 1891
462,418
Method of and Apparatus for Electrical Conversion and Distribution - Feb 4, 1891
514,168
Means of Generating Electric Currents - Aug 2 1893
Tesla used Leyden jars in his first lectures (depicted on the table), in his exhibits (two groups of jars on the left side table), and in the laboratory. His first oscillators used Leyden jars. Tesla gradually replaced the jars with oil capacitors, salt water capacitors, and large mica plate capacitors (detailed below).
Circuit diagram symbols Tesla uses for capacitance.
It had been known since Henrich Hertz that charging a capacitor, they used Leyden jars in those days, with a high-voltage static machine, then discharging the capacitor through a short coil produced oscillations. It was discovered through measurements that these oscillations were perfectly timed, and that the frequency of these oscillations were dependent on the size of the jar (capacitor), and the size of the coil. A large coil, discharging a large jar, or a bank of jars connected together in parallel, produced a lower frequency... But even these "lower frequencies" are very high compared to the operating frequencies of Tesla iron core generators, and iron shaft reciprocating oscillators. The normal operation of all of these circuits is to produce pulses at an audio frequency rate, but usually the pulses themselves are very high-frequency oscillations (exceptions below). These high-frequency oscillations are produced by energy bouncing back and forth from one capacitor plate to the other, like a spring. These high-frequency oscillations are maintained with a declining amplitude until the electrical fire, or arc, that forms in the spark gap is broken, or "quenched".
Tesla wholly embraced the concept of capacitive discharge. He developed the Hertz oscillator into a continuosly operating, pulse power output circuit. The first circuits were switched with simple air gaps, a technology that was very familiar to The Arc-Light Men. These circuits were patented (above and below) and they were repeatedly demonstrated in lectures below.
The above chart shows a non-oscillatory pulse train of the type produced by 462,418 - Fig 2 - with careful adjustment. These waveforms were researched and developed for the purpose of exciting harmonic oscillators, - motor fields, - and for pulse ground wave transmitters. But as mentioned previously, all the other circuits here are designed to oscillate, and 462,418 oscillates by default. You have to set it up carefully to get the wave train in the above figure, the air gaps have to be carefully quenched, but it can be done.
EXPERIMENTS WITH ALTERNATE CURRENTS OF HIGH POTENTIAL AND HIGH FREQUENCY
ON LIGHT AND OTHER HIGH FREQUENCY PHENOMENA
Above: Early European Tesla Coil that was made following Tesla's lectures overseas. T is an ordinary induction coil with a single layer secondary on a wooden spool, with the primary inside. It is submerged in a glass tank full of clear mineral oil. - L is the Leyden jar, "e" is the primary or "tank circuit" spark gap and E are the output terminals with high frequency Tesla energy. Not shown is a low frequency conventional type high voltage induction coil used to charge the Leyden jar.
In 1892 Tesla demonstrated a coil designed and constructed to be submerged in oil. In US Patent 514,168 - Tesla resorts to placing the entire circuit, capacitor, and the rotary switch, under oil. The importance of excluding all gas from the windings of high-frequency equipment was discussed by Martin as well as Tesla.
The classic spark gap Tesla Coil is directly descended from these patents and lecture demonstrations. These circuits as shown are designed to process power. The capacitor in the circuit accepts a high-voltage charge over a period of time. When the charge is developed, it is discharged with a switch into a short heavy coil. It takes a period of time to charge a capacitor, but the discharge is very, very rapid. Because of the rapid rate of discharge, the peak energy delivered by a capacitor can be very, very large. The oscillator performance depends on the circuit design and quality, especially the capacitor quality, and the switch.
The first switches were simple voltage triggered air gaps: when the capacitor charged, the voltage rose: the air gap was adjusted to discharge when the capacitor voltage was at or near its peak. These work pretty well for discharging the capacitor, but the switch does not want to turn off easily. Tesla immediately began developing the technology with a goal of being able to produce clean sine waves, -- "damped oscillatory" waves - and - isochronous pulse wave trains. He worked extensively on improving the switching performance. Rotary switching was introduced in lecture in 1893, and extensive patent documentation of high-precision rotary switching technology was recorded.
This [Fig above] is the apparatus I had at 35 South Fifth Avenue and also Houston Street. It shows the whole arrangement as I had it for the demonstration of effects which I investigated. This cable you see [square loop in top half of the Fig above] is stretched around the hall. These are my condensers. There is the mechanically operated break, and that is a transformer charged from the generator. That is the way I had it for the production of current effects which were rather of damped character because, at that period, I used circuits of great activity which radiated rapidly. In the Houston Street laboratory, I could take in my hands a coil tuned to my body and collect 3/4 horsepower anywhere in the room without tangible connection, and I have often disillusioned my visitors in regard to such wonderful effects. Sometimes, I would produce flames shooting out from my head and run a motor in my hands, or light six or eight lamps. They could not understand these manifestations of energy and thought that it was a genuine transmission of power. I told them that these phenomena were wonderful, but that a system of transmission, based on the same principle, was absolutely worthless. It was a transmission by electromagnetic waves. The solution lay in a different direction. I am showing you this [diagram] simply as a typical form of apparatus of that period, and if you go over the literature of the present day you will find that the newest arrangements have nothing better to show.
Nikola Tesla - New York, 1919
This was just one of many oscillator circuits Tesla used in the New York lab. The square conductor at the top of the image was a loop of cable run around the ceiling molding. The diagram inside the circuit is the rotary switch design Tesla used to switch the capacitors from charging to discharge mode. Typically in this arrangement the rotary switch was directly driven from the generator shaft. Transmitter circuits like this were first disclosed in Tesla's lecture before the American Institute of Electrical Engineers in Fig 127. The receivers Tesla developed were photographed in both the NY and Wardenclyffe laboratories. - As Tesla states, the above circuit, and others like it, are completely worthless for wireless transmitters. In order to transmit power wirelessly, the transmitter needs to produce a pure sine wave, but the circuit above produces short lived "damped waves". - But the energy developed by discharging high voltage capacitors this way is simply second to none. Tesla discovered that when the secondary coils on high frequency transformers are over-driven, the fundamental frequency of operation splits into a Harmonic Series. This is very predictable, both mathematically and practically. Tesla soon realized that these harmonics are continuous sine waves, or can be, if the circuits are set up correctly.
Receiving Table for Tesla Wireless, used in the above oscillator system.
Tesla had transmitters that worked well based on 447,920 - and - 447,921, but he was extremely limited in the power levels that could be developed with iron-shaft generators outputting between 3000 and 30,000 cycles per second. These generators had good wave forms for transmission purposes, but you could not scale them up economically without industrial support... What Tesla designed and patented was at the edge of the practical engineering limits of the time, and that is a small machine limited to about 10-25 kilowatts maximum output. If you want more output with this technology you would have to test and improve the material science and construction techniques, and then mass produce many component assemblies, like armature disks, and then synchronize them on a common shaft... It's an engineering nightmare. Tesla ended up designing large capacitors and coils to get down to the frequencies where his technology shines, and he used a Fourier Transform to convert the spike waves produced by timed capacitor discharges, into a pulsitory wave train that included a harmonic series of sine waves. This system could be used for both energy transmission and communications purposes.
Beginning in 1904, years after Tesla had gone with Harmonic oscillator technology, General Electric provided industrial support to electrical engineers like Ernst F. W. Alexanderson, who was influenced by the alternating current theories and mathematics of Charles Steinmetz, and whose work was actively promoted by Reginald Fessenden. Alexanderson, with General Electric industrial support, the nod by Steinmetz, and the promotion of Fessenden, developed high frequency motor driven alternators in the 50-60 kilowatt range which were used for transatlantic "long wave" wireless communications. These units took years to develop through trial and error, required material science improvements, and long hard thought into the construction techniques required. The end result were massive machines standing about 4-1/2 feet tall on the cast iron equipment mounts, about 12 feet long with the drive motor and gear box, and supported with pressurized cooling and lubrication systems. A progression of machines were built and installed at New Brunswick, NJ, and the transmitter there, operated by the U.S. Navy, broadcast reliably with up to 200 kilowatts output in 1918.
Tesla's Capacitor Development
As part of the development of his electrical oscillator technology, Tesla filed patents covering the improvement of capacitors (condensers) using mineral oil, a new type of capacitor with liquid electrolyte (salt water) plates, and a new method of manufacturing capacitors, coils, etc..
464,667
Electrical Condenser - Aug 1, 1891
567,818
Electrical Condenser - Jan 2, 1892
In this photo above (click image for higher resolution) of Tesla's Colorado Springs oscillator the square tanks in the foreground, mounted on insulated platforms, are large liquid electrolyte (salt water) capacitors covered under the patent above. The tanks are made from tin which was soldered up make them water tight, they form one plate of the salt water capacitor and an electrical connection was made to the tin. Inside the tank were mineral water bottles with copper terminals dropped inside and filled 2/3rds with salt water. The glass in the bottles formed the capacitor dielectric, the insulator, just like a Leyden jar. The tank was filled with salt water to a height equal to the fluid level in the bottles. The necks of the bottles, above the salt water level, were carefully cleaned and dried and then the whole works was covered in oil to insulate the glass bottle necks, suppress corona, and prevent flashovers. The carefully insulated leads from each bottle were connected together into one of three buses and brought out through three holes in the oiled wooden non-conductive covers that went over the tanks. Bottles frequently broke down under the electrical stress, the covers were removed, and the broken bottles were replaced as required. Tesla tested all of the various types of glass bottles available in sufficient quantity to complete the project, finding a brand with superior quality glass for building a large oscillator.
Above: Modern homemade salt water capactor. Many people still use glass bottles for homemade Tesla coil capacitors, but I knew a guy that ran 10 kilowatt coils with a couple of stacks of Home Depot buckets with salt water in between buckets for the plates. When the buckets were pressed together the salt water was forced up into the space between the sides of the buckets, greatly increasing the capacitance, and they never failed. They were simple, cheap, rugged, and he sealed the buckets together with silicone once he got the fluid levels correctly set. Once sealed they didn't leak. Each joint between buckets had a strip of aluminum inserted from a can that had been sanded bare. One end of the aluminum strip made contact with the brine, the middle was sealed in with silicone, and the end that stuck out had a hole in it for a nut and bolt connection to a wiring harness with ring terminals. Ten or twelve Home Depot buckets and he needed a utility distribution transformer to charge them. Modern plastic film capacitors work well when connected together into arrays, but nothing beats salt water for large very inexpensive capacitance.
577,671
Manufacture of Electrical Condensers, Coils, & Etc. - Nov 5, 1896
The equipment in the photographs below was all constructed using the technique patented in 577,671 for the manufacture of the capacitors and coils. The wooden base cabinet contains one or more high-quality mica plate capacitors which were encapsulated in a custom high-temperature sealing wax potting applied under hydraulic pressure, after vacuum pumping. The capacitor terminals come through the wooden boxes to make connections to the charging circuit, rotary switch, and primary coil.
Photos of equipment are not matched up to specific patents.
568,176
Apparatus for Producing Electrical Currents of High Frequency and Potential - April 22, 1896
568,177
Apparatus for Producing Ozone - June 17, 1896
568,178
Method of Regulating Apparatus for Producing Currents of High Frequency - June 20, 1896
568,179
Method of and Apparatus for Producing Currents of High Frequency - July 6, 1896
568,180
Apparatus for Producing Electrical Currents of High Frequency - July 9, 1896
577,670
Apparatus for Producing Electrical Currents of High Frequency - Sept 3, 1896
583,953
Apparatus for Producing Currents of High Frequency - Oct 19, 1896
Electrical Oscillators
Electrical Experimenter, July, 1919
Tesla's Electric Circuit Controllers
Precision Switching Technology
Tesla's Cymatic Research
Steam Powered Isochronous Acoustic Oscillators & Generators
Tesla Transmitters
Wireless Transmission of Electrical Energy
Tesla's Coherer Technology
Wireless Communications Receivers
Tesla's Egg of Columbus
Electrical Experimenter, March, 1919
Tesla's Laboratory Power
Boiler, Steam Engine, Line-Shaft, Belts & Pulleys
Nikola Tesla Receiver Technology
Home Appliances and Industrial Solutions
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